Micro-machined or micro-electro-mechanical systems (MEMS) devices, where there is repeated physical contact between moving parts, require lubrication to prevent the onset of stiction (static friction). This stiction can be strong enough to cause the parts to stick irreversibly together, making the devices inoperable.
For example, in the digital micromirror device (DMD™) of FIG. 1, which is one type of a MEMS device, the mirror/yoke 10/11 assemblies rotate on torsion hinges 12 attached to support posts 13 until the yoke tips 14 contact (land on) landing pads 15 located on a lower substrate layer 16. It is this mechanical contact between the yoke landing tips 14 and the landing pad sites 15 that is of particular relevance to this invention. In some cases the mirror/yoke assemblies become slow in lifting off the landing pad, affecting the response of the device and in other cases the assemblies become permanently stuck to the landing pads. One of the primary causes of stiction has been shown to be that of the landing tips scrubbing into the metal landing pads.
This “sticking” problem has been addressed by lubricating or passivating the metal surfaces of the devices to make them “slick.” Getters have been used in the device package to store the lubricants in order to maintain a low stiction environment for all moving parts over long device lifetimes. One lubricant used is powdered perfluordecanoic acid (PFDA), which tends to decrease the Van der Waals forces associated with the mirror assemblies in the DMD™ or any moving parts in a MEMS device, and thereby reduces the tendency for the mirrors to stick to the landing pads. However, PDFA has a very reactive molecule, which can react with other package constituents, causing severe damage to the device.
FIG. 2 is a drawing of a typical DMD™ device package. This shows the DMD™ 21 mounted in a package frame 20 with attached cover glass (package lid) 22. The cover glass 20 is usually made opaque 23 on the underside with a transparent aperture for optical interfacing with the device. As mentioned, this stiction problem has normally been addressed by attempting to control the environment inside the packages. For example, FIG. 3 illustrates how PFDA getters 31 and/or moisture gathering getters are attached to the underside of the glass cover 30 by means of an adhesive 32. The getters are used to both collect moisture in the package and provide lubrication (PFDA) to the moving parts in the DMD™. These getters may also be installed in empty areas within the package cavity. However, the PFDA lubricants are reactive and difficult to handle in a manufacturing environment and as a result, tend to drive up the cost of packaged MEMS devices. The moisture getters are used to control rather large amounts of moisture in the package, which should only be present if the getters themselves are misprocessed.
What is needed is a robust, non-corrosive lubricant that can be easily applied, without the use of getters, to the surface of MEMS devices to prevent the moving parts from sticking together. The fluorosurfactant lubricant of the present invention meets these requirements.